This invention is in the field of foamed or blown polymeric materials; more particularly, this invention relates to a foamed copolymer of ethylene and chlorotrifluoroethylene.
It is well known to produce foamed polymeric materials. Foamed polymeric material compositions which are of interest with regard to the present invention are disclosed in U.S. Pat. Nos.: 3,306,862; 3,347,845; 3,428,583; 3,518,332; 3,574,659; 3,725,317; 3,743,605; 3,862,963; 3,957,192; and 4,031,041.
It is known to use materials from the class of dihydrocarbyl hydrazodicarboxylates as blowing agents in polymeric materials (U.S. Pat. No. 3,888,801). This class of blowing agents has been found to thermally decompose to produce olefins, carbon dioxide, carbon monoxide, alcohols and a small amount of nitrogen. It is also known that other additives such as plasticizers, fillers, nucleating agents and the like, can be added to polymeric materials when using the hydrazodicarboxylates.
Japanese Kokai Patent Publication Nos. 25860-1977, 53964-1977, 121864-1978, and 41969-1979 relate to ethylene-ethylenetetrafluoride copolymer foam compositions. Of particular interest is Kokai Patent Publication No. 41969-1979, which discloses an ethylene-ethylenetetrafluoride copolymer which contains a nucleating agent which can include magnesium oxide and calcium carbonate; and a blowing agent which can include diisopropyl hydrazodicarboxylate. It is noted that when using nucleating agents including magnesium hydroxide and calcium carbonate, it is difficult to obtain a blown product which contains fine gas bubbles and has good surface smoothness. This publication further notes that the basic carbonates of lead, zinc and magnesium can be used as blowing agents.
The terms blowing agents and nucleating agents used herein are used in accordance with their traditional meaning in the foam plastic arts. Blowing agents are defined as chemicals added to plastics and rubbers that generate inert gases on heating, causing the resin to assume a cellular structure. Blowing agents are also known as foaming agents.
Nucleating agents are materials used to provide sites for the formation of cells resulting from the blowing agents. Nucleating agents are generally used to provide a plurality of locations for cell formation to yield a finer cell structure.